Methods of transmitting data are commonly known and performed today on a routine basis to send various multimedia data such as text, graphics, audio, video, images etc. across computer networks situated in various parts of the world. Generally the transmission process requires both hardware and software for performing its function. Typically, the hardware includes various types of personal computers and hand held multimedia data sending or receiving devices. These devices run under the control of an operating system and utilize multimedia application software programs. As is known in the art, streaming media data is data which is transmitted to a receiving computer system and presented (usually after buffering temporarily at the receiving system) and then discarded (not stored) at the receiving system.
Currently, data is sent in form of packets from one multimedia device to another. A large amount of information is required to be sent in a real-time manner in the data packets, which imposes a heavy load on the systems. Streaming media data, such as Real-Audio data in streaming media format specified by Real-Networks, is sent through the Internet is near real-time manner in many cases.
In one approach, the components involved in data transmission of streaming media are known to be a server (which may be referred to as originating server), a caching proxy server and a client. These components in various combinations communicate with each other for transmitting data packets in real-time. The communication link that currently exists between the components uses real-time transfer protocols (RTP) and real-time streaming protocols (RTSP) to communicate and send packets to each other. For this approach to work, a caching proxy server needs to communicate with the system server, receive a stream of RTP data packets, and transfer the information contained within the RTP data packets to a client. FIG. 1a shows an example of a prior method in which a caching proxy server receives streaming media data and provides this data to a client. In order to perform its function properly and efficiently, the caching proxy server needs several pieces of information from the server to be able to cache an RTP stream easily and reliably.
A problem with the current approach is that it is not able to provide some of the key required information such as data packet transmit time and video packet frame type information that a caching proxy needs to be efficient.
This information allows a caching proxy server to provide smooth packet delivery to its client by knowing the time an RTP data packet was intended to be sent, and type of video frame that is being sent without knowing the specific payload format. Another problem with the current approach is that it is not able to provide multiple pieces of unrelated data in one delivery to the caching proxy server. Furthermore, packets from the server may be “lost” and never reach the caching proxy server. In addition, there is normally no way to recreate a complete “pristine” copy at the caching proxy server.
Prior art servers communicate RTP information to the caching proxy server by sending information through a cache-control header. In one approach, a cache-control header contains normal header fields. In another approach, unrelated to cache control of RTP information, a single type of additional information has been added to the normal fields in a header extension format without specifying the type of additional information. In this approach only a single piece of RTP extension can be added to the normal field of the header and sent at any one time.
A problem with using this limited, non-extensible approach is that a server is not able to attach multiple sets of unrelated data at a time to send to the caching proxy server. Another problem with this approach is that the header extension used in these methods are still not able to provide all the information a caching proxy server needs to cache a stream properly and to transmit the stream properly. Yet another problem with this approach is that there is no way to identify the particular extension independently of other possible extensions.